Exemplary embodiments of the invention relate to a circuit layout and a method for frequency-dependent matching of a high-frequency amplifier stage according to the characteristics as specified in the independent claims.
Power amplifiers and their transistors are typically, inherently non-linear components; this means that, generally, they generate spectral content of integer multiples of the fundamental of the signal that is to be amplified, so-called overtones or harmonic partials. These overtones or harmonics negatively impact the signal spectrum in a variety of ways. On the one hand, they reduce the efficiency of the amplifier circuit, because a part of the expended DC power is not used for boosting the fundamental, as desired, but for generating power for the frequencies of the harmonics. On the other hand, they contaminate the spectrum of the amplified output signal. Depending on the application, expedient filtering is necessary to reestablish the spectral purity of the signal, for example of the radar transmission signal.
The phase response of an optimal complex load at the transistor output for achieving high efficiency in a reactively matched amplifier circuit is generally reversed over the frequency relative to the physically achievable phase response in passive matching circuits. This is why a wide-band, purely passive and non-adaptive implementation of the matching circuit always constitutes a compromise between wide-band capability, efficiency and output power.
In narrow-band implementations of amplifiers, it is possible to cut off one or a plurality of the overtones in a targeted fashion in an effort to improve efficiency (“harmonic matching”). However, this method is inapplicable for wide-band circuits, particularly those covering several octaves, because, in this context, the harmonics that must be suppressed fall within the useful band of the circuit and may, therefore, not be attenuated.
Tunable filters can be used for suppressing undesired spectral content, such as harmonics. However, due to the fact that these filters reflect the harmonics, they have a frequency-dependent feedback on the power amplifier and thus influence the properties of the same, with negative effects on the efficiency of the amplifier. Moreover, they themselves demonstrate great attenuation effects, particularly at high frequencies, that further reduce the efficiency of the total system.
German patent document DE 24 12 920 A1 discloses a circuit layout and a method for influencing signals that are to be transmitted in a frequency-dependent manner.
Exemplary embodiments of the present invention provide a wide-band amplifier circuit that suppresses undesired harmonics of an amplified signal and improves the efficiency of the amplifier circuit. Exemplary embodiments of the present invention also provide a method for suppressing undesired harmonics of an amplified signal, while simultaneously increasing the efficiency of the amplifier circuit.
The circuit layout for frequency-dependent matching of a high-frequency amplifier stage according to the invention comprises an HF amplifier stage, where an HF total path, which routes the total frequency band, is divided at the output into a plurality of partial frequency paths (referred to below as partial paths) for the respective preset partial frequency bands and, after the processing of the partial frequency bands in the partial paths, these partial paths are reunited into the high-frequency total path. According to the invention, the partial paths comprise a pass-filter on the input side and a pass-filter on the output side for a preset partial frequency band, respectively, as well as a matching network for matching the amplifier stage in the preset partial frequency band. According to the invention, at least one partial frequency path is switchable, when a control signal is supplied thereto.
In one advantageous embodiment of the invention, the partial frequency path can be grounded. Expediently, at least one switch is provided on the input and output sides of the matching network of a partial frequency path, such that, upon supplying a control signal, the switch shorts the partial frequency path to ground, whereby signals in this partial frequency path are reflected.
In one further advantageous embodiment of the invention, at least one partial frequency path can be decoupled from the circuit layout, when a control signal is supplied. Expediently, the decoupling action is achieved by the use of one or several multi-circuit switches that are inserted in the at least one partial path.
In other words, the circuit layout according to the invention is based on the idea of dividing the total useful band of the HF amplifier into two or more partial bands and of distributing the output signal of the HF amplifier, for example of a transistor, over two or more partial paths (channels), preferably using a frequency-dividing network (a duplexer or triplexer, etc.) depending on the partial frequency band. In each partial path, the corresponding spectral content of the output signal is processed in a matching circuit. Undesired spectral content can be shorted to ground the respective partial path or suppressed by opening alternate multi-circuit switches in the respective partial path; and they are thus no longer consequential for the HF total signal, after the individual partial paths have been reunited into the total HF path.
In contrast to a circuit layout according to the prior art, where a single matching circuit covers the total bandwidth in a non-adaptive manner, the circuit layout according to the invention allows for better approximation of the optimum load for maximum efficiency. Furthermore, there exists the possibility of expediently terminating not only the fundamental but also the harmonics to achieve maximum efficiency. For example, if a standard bandwidth (“fractional bandwidth”) that is greater than 2:1 is to be implemented, when dividing the total HF path into a lower and an upper partial path, the matching circuit for the upper frequency band is also, additionally, switchably configured in order to be passable, depending on the frequency range of the signal that is to be amplified, either for high frequencies or, when the signal that is to be amplified is in the lower partial band, to expediently terminate the harmonics that are generated by the amplifier stage. Moreover, dividing the total useful band into two or several partial bands also results in a reduction of the complexity of the individual matching networks within the partial paths relative to the complexity of a single matching network for the total bandwidth; as a consequence, fewer passive components, such as coils, capacitors and impedance-transforming lines are needed, thus resulting in fewer losses in the matching networks of the individual partial paths.
Using the circuit layout according to the invention, dependent on the frequency of the fundamental that it to be amplified, the HF amplifier stage is always offered the optimally suited complex load both for the fundamental as well as the harmonics, which is necessary for maximum effectiveness of the total system. Due to the fact that, when the total band is divided into the individual partial bands thereof by means of the frequency-dividing network that is preferably employed, it is not obvious as to whether a spectral content of a partial band is in fact the desired amplified signal of the fundamental that is to be amplified or as to whether this spectral content is in fact the undesired harmonic of a signal that is to be amplified in a lower frequency band; as a remedy, a control signal for the suppression of harmonics, is supplied at least to one partial path, preferably several partial paths, and wherein the control signal was generated, for example, in a signal processing electronics unit.
The method according to the invention is substantially characterized by the fact that a control signal is supplied to at least one partial frequency path, and that this at least one partial frequency path is shorted to ground; or by the fact that, by way of a variant of the invention, the same is decoupled from the rest of the invention. Expediently, the control signal is supplied to that partial frequency path that contains an undesired harmonic of the signal that is amplified by the high-frequency amplifier stage. This undesired harmonic is eliminated by the method according to the invention in the total band of the signal that is amplified by the HF amplifier stage.